Oblique penetration modeling and correlation with field tests into a soil target

An oblique penetration modeling procedure is evaluated by correlation with onboard acceleration data from a series of six penetration tests into Antelope Dry Lake soil at Tonopah Test Range, Nevada. The modeling represents both the loading which is coupled to the penetrator bending and the penetrator structure including connections between the major subsections. Model results show reasonable agreement with the data which validates the modeling procedure within a modest uncertainty related to accelerometer clipping and rattling of the telemetry package. The experimental and analytical results provide design guidance for the location and lateral restraint of components to reduce their shock environment

Contact Maturing and Aging of Silica Sand

For more than three decades, sand has been observed to alter its engineering properties over time, but no consensus has been reached on the driving mechanisms behind this phenomenon. Silica sand freshly deposited or after recent disturbance tends to undergo delayed changes in small strain stiffness, penetration resistance, or liquefaction resistance. In the same category of phenomena is a delayed increase of the shaft resistance of displacement piles after installation (pile setup). Micromechanical behavior at grain scale and the contact scale is coming to be understood as the most plausible mechanism among the proposals suggested in the available literature, but only very limited research has been conducted at the contact scale in studies of sand aging. A static fatigue hypothesis is advocated in this thesis; it suggests that delayed fracturing of micro-morphological features on grain surfaces at contacts, such as asperities and mineral debris, is a key contributor to aging of silica sand. The static fatigue process at inter-grain contacts induces changes in micromechanical properties of the contacts, a process termed maturing in this research, and it triggers rearrangements of sand grains over time. Maturing of contacts and rearrangement of grains are hypothesized to be the cause of the observed changes in macroscopic engineering properties of sand over time. To support this hypothesis, this research focuses on exploring micromechanical behavior of inter-grain contacts through micro-scale experiments complemented with numerical simulations. The following major tasks were accomplished: (1) Micro-scale laboratory experiments were conducted to study time-dependent response of inter-grain contacts under sustained loads; they produced the first set of data of its kind. (2) Laboratory experiments on sand grain assemblies were performed to provide evidence that the contact behavior induces aging effects in sand; factors affecting rates of aging, such as loads, pore fluid acidity and grain sizes were explored. (3) Simulations of a single inter-grain contact were performed with the distinct element method, and possible consequences of contact fatigue/maturing were demonstrated. (4) Finally, a preliminary finite element framework was developed to explore the evolution of grain surface textures to shed light on the effects of pore fluid chemistry on aging rates.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136992/1/zjwang_1.pd

DEVELOPMENT OF ADVANCED PAVEMENT MATERIALS SYSTEM FOR BLAST LOAD

Ph.DDOCTOR OF PHILOSOPH

The uplift of high voltage transmission tower foundations

The in-service performance of transmission tower foundation systems is poorly understood. This knowledge deficiency is particularly acute with regard to the dynamic and transient loading of these foundations in uplift. There is also uncertainty surrounding the integrity of existing assets as design practice appears to overestimate the capacity of the foundations when they are subject to testing. A significant component of cost of new high voltage overhead line route construction or uprating involves the maintenance or reinforcement of the individual transmission tower foundation systems. Therefore, a more developed understanding of the foundation system behaviour is required to facilitate these works in a cost-effective and timely manner. To gain a better understanding of foundation system performance, a series of full scale rapid uplift tests were carried out in July 2012. The tests bridged understanding of the load-displacement, load-rate and rate effects of soils from previous experimental research to field scale, with associated construction and in situ soil nonlinearities. The tests made use of modern instrumentation and monitoring techniques in combination with rigorous numerical finite element back analysis to update understanding of in situ failure mechanisms and capture uplift capacity enhancements due to the application of rapid loading. The field tests and numerical back analysis results highlighted significant limitations in current design practice particularly the reliance on an outdated failure mechanism and ultimate limit state criterion. The results of the rapid uplift tests compared to standard industry practice suggested that the latter method may be unduly conservative leading to an underestimation of in-service capacities. The results presented will lead to a better understanding of foundation system performance and more legitimate design and testing practice technical specifications

An investigation of stress wave propagation through rock joints and rock masses

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, Laboratório Nacional de Engenharia Civil. 201